This invention relates to an electrolytic apparatus with a liquid throttle unit that establishes non-contacting sealing between a strip and a liquid electrolyte during electrolytic plating, of the surface of a metal strip, with tin, zinc, chromium or other metal or during pickling or other surface treatment.
Numerous methods and apparatuses have been proposed for electrolytic plating of the surface of a metal strip with tin, zinc, chromium or other metals. Recently, particular demand has arisen for high-efficiency, high-speed plating equipment that offers high performance in excess of 500 m/min. For such high-speed plating, however, a specific requirement must be met, because, in the vertical type plating apparatus, the strip passes vertically and the running strip penetrates a portion of the cell body at its bottom end, while in the horizontal type plating apparatus the strip passes horizontally and the running strip laterally penetrates a center portion of the cell body. In order to conduct the plating (including pickling and other treatments) while continuously moving the metal strip to be plated, it is therefore necessary to seal the penetrated portion so as to prevent leakage of the treatment liquid. This is because the constant running state of the strip results in the plating treatment liquid also being leaked as an entrained flow along the running strip surface.
Specifically, as shown in FIG. 1, the amount of plating treatment liquid leakage owing to entrained flow is proportional to strip running speed. It was found that at a strip running speed of around 200 m/min, the amount of plating treatment liquid leakage (loss) rises to 20% or more of the fed treatment liquid, at a strip running speed of about 500 m/min, it reaches 80% or higher, and at 1000 m/min, the maximum strip running speed currently conceivable, the amount of leakage reaches nearly 100%. With such increasing leakage, the amount of treatment liquid fed must be increased to continue operation with the plating treatment cell kept constantly full.
Sealing methods for preventing treatment liquid leakage include one, such as taught by JP-A-(unexamined published Japanese patent application)5-331695, in which a pair of damrolls are installed one on either side of the strip pass line to be rotatable in contact with the strip surface, the opposite axial ends of the damrolls are sealed by seal rings from the outside, and seal plates are installed for sealing by contact with the peripheral surfaces of the damrolls. This method, which is an improvement on the well-known rotating seal system, enables the sealing capability with respect to the strip surface to be increased substantially in proportion to the squeezing force between the damrolls.
FIG. 12 illustrates a vertical type electrolytic apparatus disclosed by JP-A-5-171495. As shown, liquid electrolyte 103 is fed between a strip 100 and electrodes 101, 102 to impart an agitation effect between the strip and the electrodes. In addition, liquid seal devices 104a and 104b equipped with seal rolls 105a, 105b are installed at the lowermost portion of the vertical type electrolytic apparatus for preventing runoff of the liquid electrolyte 103, thereby obtaining a high current density while maintaining the level of the liquid electrolyte.
As shown in FIG. 13, a vertical type electrolytic apparatus disclosed in JP-A-60-56092 (U.S. Pat. No. 5,236,566) imparts an agitation effect between a strip 115 and a liquid electrolyte 110 by using liquid feed nozzles 113 and 114 to feed liquid electrolyte into spaces between electrodes 1.11 and electrodes 112 immersed in the liquid electrolyte 110.
In the method of squeezing the strip with damrolls, however, the strip surface tends to be easily scratched. One reason for this is that the squeezing force of the rolls on the strip has to be maintained high in order to secure sealing pressure. Another is that contact scratches are produced between the strip and the roll surfaces owing to mismatching between the strip running speed and the circumferential speed of the rolls. What happens most often, however, is that sludge carried in from the exterior and, particularly in the electrolytic cell, foreign matter such as electrolytic deposits, get into the treatment liquid and lodge between the strip surface and the damrolls to become sources of scratching. This lowers production yield, degrades quality, makes more frequent roll inspection and exchange necessary, and leads to a decline in production line operating rate. In a case where the strip passes between the seal rolls while running in a meandering state, moreover, if the strip should snake in the manner of weaving in the axial direction of the rolls, then, since the strip is squeezed between the rolls, the portions of the strip strongly squeezed by the rolls pass with no freedom in the thrust direction, thereby producing wrinkles in the strip. This, in conjunction with the aforesaid biting of foreign matter, further markedly degrades quality.
In the aforesaid vertical type electrolytic apparatus, achievement of electrolytic plating at high current density during high-speed strip streaming of the strip requires efficient feeding of metallic ions to the plating surface and rapid removal the large quantity of gas produced by the high-current-density electrolysis from between the electrodes. The problems posed by these needs have not yet been solved. The vertical type electrolytic apparatus disclosed by JP-A-5-171495 (FIG. 12) still has the following problems:
1) Since the liquid electrolyte 103 is retained solely by electrode units formed by the electrodes 101 and 102 and, furthermore, prevention of liquid electrolyte runout is conducted by the pair of seal rolls 105a, 105b, the loads on the liquid seal devices 104a, 104b are excessive, making liquid retention difficult during high-speed strip streaming.
2) Scratching owing to slipping between the strip 100 and the seal rolls 105a, 105b is liable to occur during high-speed strip streaming and scratching is also produced by foreign matter pressed onto the strip after lodging between the strip and seal rolls.
3) Since the seal rolls themselves experience damage and wear that degrades their liquid seal performance and leads to increased liquid electrolyte leakage, the flow rate required at the electrodes for plating becomes hard to secure and defective plating therefore arises owing to uneven liquid electrolyte flow.
On the other hand, the vertical type electrolytic apparatus disclosed by JP-A-60-56092 (FIG. 13) conducts plating with the electrodes 111 and 112 immersed in the liquid electrolyte 110 and can adequately handle currently used strip running speeds. However, if the strip running speed should be raised to a high level without implementing some measure such as installation of a liquid throttle device or the like, the loss owing to the entrained flow caused by movement of the strip 115 will, as shown in FIG. 1, increase with increasing running speed of the strip, namely, will accelerate up to and reach substantially 100% at around 500 m/min. Even if the strip running speed is further increased to around 1000 m/min, the loss by entrained flow will remain saturated. When this phenomenon occurs, the flow rate between the strip 115 and the electrodes 111, 112 becomes hard to secure and plating defects such as burnt deposits occur.
The present invention was made to overcome the foregoing problems. One of its objects is to provide a method for prevention of plating treatment liquid leakage and utmost avoidance of strip surface scratching and wrinkling. Another of its objects is to provide an electrolytic apparatus with a strip non-contacting liquid throttle unit that can facilitate inter-electrode liquid retention during high-speed strip streaming, prevent clinging of the strip to the electrodes, and enhance plated product quality and plating operation efficiency.
A first aspect of the present invention for achieving these objects provides an electrolytic apparatus with a strip non-contacting liquid throttle unit that, in a method of passing a strip between paired members of a liquid throttle unit provided on at least one of an inlet side and an outlet side of a treatment cell through which the strip is continuously passed, is characterized in that a spacing between the paired members of the liquid throttle unit is set very slightly larger than the thickness of the passed strip to maintain the surfaces of the strip and the liquid throttle unit in a non-contacting state.
A second aspect of the present invention provides an electrolytic apparatus with a strip non-contacting liquid throttle unit according to the first aspect of the invention, characterized in that the paired members of the liquid throttle unit are seal mechanisms and the seal mechanisms comprise at least one means among a pair of seal rolls, a pair of seal blocks and a pair of wedge-shaped seal blocks.
A third aspect of the present invention provides an electrolytic apparatus with a strip non-contacting liquid throttle unit according to the first aspect of the invention, characterized in that the liquid throttle unit is a pair of nozzle devices for jetting and circulating treatment liquid in the treatment cell.
A fourth aspect of the present invention provides an electrolytic apparatus with a strip non-contacting liquid throttle unit according to the first, second or third aspect of the invention, characterized in that the spacing between the passed strip and the pair of seal mechanisms or the nozzle mechanisms is 0.1 mm-5 mm, preferably 0.3 mm-2 mm, larger than the sheet thickness.
A fifth aspect of the present invention provides an electrolytic apparatus with a strip non-contacting liquid throttle unit that, in a method of passing a strip between a pair of seal rolls provided on at least one of an inlet side and an outlet side of a treatment cell through which the strip is continuously passed, is characterized in that a spacing between the pair of seal mechanisms is set 0.1 mm-5 mm, preferably 0.3 mm-2 mm, larger than the sheet thickness to establish a non-contacting relationship between surfaces of the strip and circumferential surfaces of the seal rolls, treatment liquid is throttled in spaces formed by the seal rolls to diminish in the direction of strip advance, and thin film layers of treatment liquid in the treatment cell are formed between the strip surfaces and the circumferential surfaces of the seal rolls to produce a sealing capability with respect to the treatment liquid.
A sixth aspect of the present invention provides an electrolytic apparatus with a strip non-contacting liquid throttle unit according to the fifth aspect of the invention, characterized in that a drive system for rotating the seal rolls is adopted that matches the direction of rotation with the passing direction of the strip and makes the circumferential speed of the seal rolls identical to the running speed of the strip to synchronize the operations of the strip and the seal rolls.
A seventh aspect of the present invention provides an electrolytic apparatus with a strip non-contacting liquid throttle unit that, in an electrolytic apparatus in which a strip is run through an electrode unit formed between electrodes disposed at prescribed spacing, a liquid feeding unit provided on an outlet side of the electrode unit passes liquid electrolyte to the electrode unit to conduct electrolytic treatment, liquid electrolyte after electrolytic treatment is recovered by a waste liquid unit provided on an inlet side of the electrode and a liquid electrolyte tank is provided on the inlet side or the outlet side of the electrode unit to communicate and connect with the electrode unit through the liquid feeding unit or the waste liquid unit, is characterized in that a liquid throttle unit adjacent to the electrode unit and the liquid electrolyte tank filled with liquid electrolyte is a pair of seal mechanisms or nozzle devices spaced facing each other in a non-contacting state with a passed strip and the spacing between the seal mechanisms or the nozzle devices is 0.1 mm-5 mm, preferably 0.3 mm-2 mm, wider than the thickness of the passed strip.
An eighth aspect of the present invention provides an electrolytic apparatus with a strip non-contacting liquid throttle unit that, in an electrolytic apparatus in which a strip is run through an electrode unit formed between opposed electrodes disposed at prescribed spacing, a liquid feeding unit provided on an outlet side of the electrode unit passes liquid electrolyte to the electrode unit to conduct electrolytic treatment, liquid electrolyte after electrolytic treatment is recovered by a waste liquid unit provided on an inlet side of the electrode and a liquid electrolyte tank is provided on the inlet side or the outlet side of the electrode unit to communicate and connect with the electrode unit through the liquid feeding unit or the waste liquid unit, is characterized in that a liquid throttle unit adjacent to the electrode unit and the liquid electrolyte tank filled with liquid electrolyte is formed of two laterally symmetrical seal blocks, preferably wedge-shaped seal blocks, which face each other across a space that diminishes in the direction of strip advance and maintain a non-contacting state with a passed strip, the spacing between the seal blocks being 0.1 mm-5 mm, preferably 0.3 mm-2 mm, wider than the thickness of the passed strip.
A ninth aspect of the present invention provides an electrolytic apparatus with a strip non-contacting liquid throttle unit according to the eighth aspect of the invention, characterized in that the wedge-shaped blocks are equipped with a liquid feeding system for feeding liquid electrolyte from surfaces facing the strip toward the strip over the full width of the strip.